This invention relates generally to large diameter flexible pipe for example, plastic pipe, used in underground drainage systems and more particularly to a pipe having a reinforcing and strengthening preassembled drainage line member containing lightweight aggregate placed on the outside of the pipe to prevent deformation of the pipe under load and to resist deflection and provide impact resistance during shipping and handling of the pipe and placement of the pipe into a trench. Normally gravel is placed around the pipe in the trench. The lightweight aggregate replaces the gravel and enhances drainage around the pipe while providing structural support thereto.
In recent years thin walled, cylindrical plastic pipe constructed of high density polyethylene (HDPE) has been successfully substituted for prior concrete and metal pipe in constructing drainage systems for culverts, cross drains, storm sewers, land fills, and other public and private construction. The diameter of the larger pipes range from about 12 inches to 60 inches and are manufactured in about 20 foot lengths. Depending upon the application the pipes may be corrugated both internally and externally, corrugated externally with a smooth interior surface or provided with both smooth interior and exterior surfaces. The depth at which these pipes can be buried is from about 12 inch soil cover to as much as 60 foot soil cover.
These large diameter plastic pipes are subjected to various forces during transit from a manufacturing facility or a warehouse to a job site and while the pipe is being handled at the job site which tend to distort the pipe from its normal circular cross section. Although the pipe is reasonably rigid the forces may tend to flatten, bend or dent the pipe. Similarly, once the pipe is installed in the underground trench and the pipe is then covered with the backfill material, the weight of that material may deform the pipe from its normal circular cross section to an out of round condition. In addition, once in place and covered by gravel and fill, vehicles driving over the pipe, e.g. when the pipe is buried under a road, subject the pipe to substantial loads which tend to deform the pipe.
It would be advantageous to provide such large diameter flexible plastic pipe with a system which alleviates those deflection and deformation problems while facilitating drainage around the pipe and the invention as described hereinbelow was developed for that purpose.